Interrogating system for subscription television receivers



4 Sheets-Sheet 1 Aug. 6, 1968 M. c:A HENDRICKSON ET Al- NTERROGATING SYSTEM FOR SUBSCRIPTION TELEVISION RECEIVERS Filed July 1, 1964 Aug. 6, 1968 M. c. HENDRICKSON ET AL 3,396,232

INTERROGATING SYSTEM FOR SUBSCRIPTION TELEVISION RECEIVERS 4 Sheets-Sheet 2 Filed July l, 1964 Aug 6, 1968 M. c. HENDRICKSON ET Ax. 3,396,232

INTERROGATING SYSTEM FOR SUBSCRIPTION TELEVISION RECEIVERS Filed July l, 1964 4 Sheets-Sheet 5 O O O D n F; l l N l 'd n 2 O D v .E n E ID C 'E un C E mfENTORS li I 1 MELVIN c. HENDRICKSON GEORGE V. MORRIS IG3OQUJLL D I-a! .J o

.H MQW f fm2 ATTORNEY Aug- 6, 1968 M. c. HENDRICKSON ET AL 3,396,232

LNTERROGATING SYSTEM FOR SUBSCRIPTION TELEVISION RECEIVEHS Q un 8 Q Q z no m c l` n' 522 ggD r 2y? Q E Q' s v o Q Q o 3 v go si wu M n @o l, :qu Ln o a gu* Il C m m ...l h

8 c INVENTORS l5 MELVIN C. HENDRICKSON t GEORGE V. MORRIS o .C (l) BY C( "7 l ATTORNEY 3,396,232 INTERROGATING SYSTEM FOR SUBSCRIPTION TELEVISION RECEIVERS Melvin C. Hendrickson, Elmhurst, and George V. Morris, Norridge, Ill., assignors to Zenith Radio Corporation,

Chicago, Ill., a corporation of Delaware Filed July 1, 1964, Ser. No. 379,690 30 Claims. (Cl. 17g-5.1)

ABSTRACT OF THE DISCLOSURE A plurality of subscription television receivers are sequentially examined from a central oiiice to determine those that have been tuned to reproduce a subscription television program. Each receiver includes a timing mechanism which advances, `when the receiver is appropriately adjusted to utilize the program signal, from a reference condition to a starting condition. In response to an interrogating signal, subsequently received from the central oice, the timing mechanism is advanced lfrom its starting condition and through each one of a series of dil-ferent conditions in time sequence. When the timing mechanism at each receiver reaches a p-reassigned condition, unique to the receiver, a reply signal is transmitted Iback to the central oiice with a time separation from the intenrogating signal which is unique to the receiver.

This invention relates to an interrogating system for examining a plurality of subscription television receivers from a central oliice to `determine the specic ones of the receivers which have been appropriately adjusted to receive and utilize any given subscription television program signal.

Arrangements have been developed for interrogating or sensing different subscription television receivers in a system to permit an equitable assessment of charges to each subscriber based on the subscription programs actually viewed. Unfortunately, most of those prior arrangements require relatively complex, and consequently expensive, circuitry and equipment in order to achieve accurate interrogation. On the other hand, there are other sensing systems that are not quite so complicated and costlybut they have proven to be most unreliable in that they -do not always correctly determine the specic receivers that have been adjusted to view or utilize each subscription television program. This shortcoming particularly plagues the interrogating systems of the type in which the receivers are examined from, and reply to, the central oiiice in time sequence by means of synchronously operated transponders at the receivers. It has been diicult in prior systems to insure that the receivers always reply in the correct sequence.

It is, therefore, an object of the present invention to provide a new and improved interrogating system for subscription television receivers which not only is relatively inexpensive but provides accurate and reliable results.

In accordance with one aspect of the invention, an interrogating system is provided for examining from a centra] oice a plurality of subscription television receivers, each of which includes a control that must be -acuated by a subscriber in a predetermined manner to effect utilization of a received subscription television program signal, to determine the particular ones of the receivers that have been so actuated. Each given one of the subscription television receivers comprises a timing mechanism which is adapted to be advanced from a reference condition to a startin-g condition and then to and through each one of a multiplicity of different conditions in time sequence. There are means responsive to such actuation of the control in the given receiver for advancing the timing mechanism from its reference condition to its starting condition and 3,396,232 Patented Aug. 6, 1968 for holding the mechanism in its starting condition. Means are provided Which respond to an interrogating signal, received from the central oihce, for advancing the timing mechanism from its starting condition and through each one of at least some of the multiplicity of different conditions. Finally, the given receiver includes means operable when the timing mechanism subsequently reaches a predetermined condition, which condition is unique t0 the given receiver, for transmitting a reply signal back to the central oice, the time interval between the interrogating signal and the reply signal thereby `being of a duration unique to the given receiver to indicate at the central ofce that the reply signal originated at the given receiver.

Subscription television receivers, of the type requiring a particular adjustment of a control on the part of a subscriber before a selected television program may be Watched, usually contain an enabling means of some sort which becomes operative in response to the proper adjustment of the control to elTect enabling of the receiver and consequent utilization of the subscription television program signal. When such a receiver is subject to being monitored or interrogated, there may be times when it would be desirable or beneficial to remotely actuate the enabling means `from the geographically remote central oice in order that the receiver may be disabled. For example, if the interrogation of the receiver effectively determines whether the enabling means is operable, to the end that subscription charges are based on the total enabling time and thus on the extent of use of each program signal, it is advantageous to remotely actuate the enabling means at each receiver at the conclusion of each subscription program to release or disable all of the receivers. In this Way, a subscriber will not be charged for an immediately succeeding program unless he actually wishes to subscribe to it, in which case a Apositive act on his part will Ibe required-such as a respositioning of the adjustable control.

It is therefore a further object of the invention to provide a subscription television receiver interrogating system in which a receiver may be remotely ldisabled from a central otlice.

A still `further object of the invention is to provide an interrogating system in which any selected one of the receivers may be remotely disabled from a central ollice without aitecting the other receivers inthe system.

Moreover, it is still another object to effect such selective disablement over a common conductive connection which connects all of the receivers to the central oice in parallel.

A subscription television receiver, constructed in accordance with another aspect of the invention, therefore comprises enabling 'means responsive to actuation of the control in the given receiver in the predetermined manner for enabling the given receiver to utilize the subscription television signal. Means respond to the actuation of the control for transmitting a signal to the central ofiice to provide an indication that the given receiver is utilizing the subscription television signal. Means, adapted to be remotely controlled 4from the central oice, disable the given receiver.

When a timing mechanism is employed in the transponder of each of the subscription television receivers in an interrogating system, in order to permit the receivers to respond or reply to an interrogating signal in sequence and in accordance with a predetermined schedule, it is imperative that all of the timing mechanisms operate in precise synchronism. If the timing apparatus in any re ceiver is out of step it will return a reply signal to the central oce at the wrong time and provide a false indication of use. In other words, since the receivers should reply in sequence, a reply signal from 4a receiver out of sequence results in an inaccurate charge assessment. While the present invention, with regard to 'accuracy of results,

constitutes a significant advancement over prior interrogating systems in which the receivers are sequentially examined, there is a very remote possibility that a timing mechanism in one or more of the receivers will malfunction. It therefore would be helpful to provide some arrangement for Chee-king the operation of the timing mechanisrn at each receiver to make certain that they are -functioning properly and in synohronism. It is an additional object of the invention to provide an arrangement for effectively testing the operation of a timing mechanism in a receiver, which is interrogated, to determine if the mechanism is performing properly.

A subscription television receiver, constructed in accordance with a further aspect of the invention, therefore includes a timing mechanism which is adapted to be advanced, responsive to actuation of the control in the given receiver in the predetermined manner and responsive also to an interrogating signal received fr-om the central office, from a starting condition and through each one of a multiplicity of different conditions in time sequence and in accordance with `a predetermined schedule. The receiver also includes means for determining whether the operation of the timing mechanism is adhering to the predetermined schedule.

According to a still further aspect of the invention, the receiver includes means adapted to be remotely controlled from the central office, in the event that lthe operation of the timing mechanism fails to adhere to the predetermined schedule, for disabling the receiver. Moreover, means are adapted to be remotely controlled from the central ofiice for subsequently re-enabling the receiver.

The features of this invention which are believed to be new are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood, however, by reference to the following description in conjunction with the accompanying drawings, in which:

FIGURE l is a block diagram representation of the central office and television transmitting equipment of an interrogating :system constructed in accordance with the invention;

FIGURE 2 schematically illustrates a subscription television receiver, including transponding equipment, constructed in accordance with the invention 'and capable of being interrogated by the central office of FIGURE 1;

FIGURE 3 shows various idealized signal wave forms useful in explaining the operation of the system of FIG- URES 1 and 2; and,

FIGURE 4 illustrates a portion of the system of FIG- URES 1 and 2 in order to facilitate a simplification in the explanation of one of the features of the invention.

Turning now to the structural details of FIGURE 1, block illustrates a source of conventional A.C. line voltage prevalent throughout the United States, namely a power supply for providing 120 volts, 60 cycles per second alternating current. One output terminal of line voltage source 10 is grounded while the other is connected to the movable contact 11 of a simple manually adjustable two-position switch 12. Fixed contact 13 of switch 12 is connected to one of the input terminals of a 20 cycles per second square wave voltage source 16, whose other input terminal is grounded. Stationary contact 14 of switch 12 is connected to one input terminal of a reset pulse generator 17, the other input terminal of which is grounded. Source 16 may comprise a cascade arrangement of a full wave rectifier and three flip flops or bistable multivibrators. With switch 12 positioned as shown, the full wave rectifier produces, from the output of power supply 10, 120 positive polarity pulses per second. The first two fiip ops are arranged with a feedback connection to effect a 3:1 pulse division in order that 40 positive pulses per second will be supplied to the last or third flip fiop which in turn effects a normal 2:1 division. In this way, the output of the third fiip flop, which is the output of source 16, constitutes 'a square wave of 20 cycles per second or 20 positive polarity pulses per second.

The output circuit of voltage source 16 connects to the input terminals of a fifteen count timing pulse generator 2t) which lhas l5 output terminals or taps numbered 1-15 respectively in addition to a common grounded output terminal. Timing pulse generator 20 may include a well known ring counter which has a multiplicity of stable operating conditions and may be advanced from one condition to the next in response to successively applied pulses from voltage source 16. Specifically, generator 20 has lfifteen counting stages and thus fifteen stable operating conditions. Each of the fifteen output terminals of generator 20 is connected to an assigned one of the fifteen stages in the ring counter to receive a pulse when the assigned stage is triggered. In other Words, and assuming that generator 20 is initially established in its fifteenth condition which will be considered its reference or reset condition, the very first positive polarity pulse from voltage source 16 causes the generator to assume its first stable operating condition at which time a pulse is developed at output terminal or tap 1. In response to the next succeeding lfourteen positive pulses from :source 16, generator 20 is successively actuated through its secondfifteenth stable conditions to produ-ce pulses on taps 2-15 in sequence. In response to the sixteenth pulse from source 16, generator 20 cycles back to its first condition to produce a pulse at tap 1, and another counting sequence commences.

In this way, output tap 1 effectively produces the first pulse received from source 16 and every fifteenth pulse thereafter, output tap 4 receives the fourth pulse from source 16 and every fifteenth pulse thereafter, output terminal 12 the twelfth pulse and every fifteenth pulse thereafter, while output tap 15 produces the fifteenth pulse from source 16 .and every fifteenth pulse thereafter. Generator 20, after being triggered to one of its stable operating conditions by a positive pulse from source 16, remains there until the next succeeding positive pulse. Hence, generator 20 will be established in each of its conditions for one complete cycle of the squarewave from source 14S-namely 1/20 or .05 of 'a second. The duration of each pulse at the fifteen output taps will therefore be twice that of each positive pulse from source 16.

Since each of the fifteen output taps of generator 20 produces only one pulse for every fifteen received from source 16, the pulse repetition or recurrence frequency at each of those taps is 20 divided by 15 or 1.33 pulses per second. In other words, a pulse (.05 second or 5() milliseconds wide) is developed at each of the fifteen output taps every .75 second or 750 milliseconds.

Output tap 15 of timing pulse generator 20 is connected to one terminal of the tape advance magnet 23, whose other terminal is grounded, of a conventional motorized paper tape punch 24. For example, unit 24 may be a Fridens motorized paper tape punch, Model 2, manufactured by Friden, Inc. It contains a quantity of paper tape on which information is recorded in the form of punched holes. Magnet 23 is energized in response to each pulse from output tap 15 of generator 20 to effect re-positioning of the tape so that a new tape area will be adjacent the punching or recording mechanism.

Output tap 15 of generator 20 is also connected to a 400 magnetic impulse counter 28. This counter may be of conventional construction and counts the number of pulses received from generator 20. It also includes a threedigit visual count display, like an odometer, so that at all times an operator in the central ofiice will know the number of pulses counted from a zero reference, which, as will be made apparent, will indicate to the operator which particular one of the subscription television receivers in the system is being interrogated at any given time.

As illustrated, the system is calculated to monitor or interrogate 399 different receivers in time sequence. As will be seen, 4a different receiver is examined every 3%: or .75 second. Counter 28, after being reset in a manner to be explained to display the number 000, counts 399 successive pulses from timing generator 20 and with each count a corresponding number in the series 1-399 is visually displayed. In other words, the tirst pulse effects the display 001, the second pulse 002, and so forth. The 400th pulse resets counter 28 back to the 000 display.

The numbers 1399 are respectively assigned to the 399 different receivers in the system as identification numbers and represent the sequence in which the receivers are examined-receiver No. 1 being interrogated first, receiver No. 2 second, receiver No. 3 third, etc. Since the pulses from the generator 20 occur at the rate of one every .75 second, a period of 300 seconds (400 multiplied by .75) or 5 minutes Will be required to cycle counter 28 from 000 to 399 and then back to 000, and of course this is the period that will be required to interrogate all 399 different subscribers. As Will be seen, in the first .75 .second of the tive-minute interrogation or scanning cycle no receiver is monitored. Receiver No. 1 is not interrogated until the second .75 second interval of the interrogation cycle. For this reason only 399 receivers are monitored in 5 minutes-receiver No. 399 being checked in the last .75 second interval.

After the 400th pulse from generator 20 resets counter 28 to the 000 display, succeeding pulses are then counted by counter 28 in the same manner as the first series of 399.

The fifteenth tap of timing pulse generator 20 is also connected to one input terminal of a 400 count timing pulse generator 30 which may take the same form as timing pulse generator 20 except that it is provided with 400 different counting stages, having 400 different stable operating conditions, so that 400 successive input pulses -are required to complete one cycle of operation. Generator 30 had 400 different output taps or terminals each of which is connected to an assigned respective one of the 400 counting stages. Assuming that generator 30 is initially reset to its 400th stable operating condition, the first occurring pulse from pulse generator 20 effects actuation of timing pulse generator 30 to its first operating condition in which a pulse is produced at output tap 1, the next succeeding pulse from generator 20 results in the development of a pulse at output tap 2 of generator 30, the third pulse produces a pulse at output tap 3, etc., until the 400th pulse from generator 20 occurs at which time a pulse is produced at output tap 400 of timing pulse generator 30. Since generator 30 changes conditions in response to successive pulses from generator 20, which occur at intervals of .75 second, the duration of each pulse at the output taps 1-400 will be .75 second.

The 401st pulse from generator 20 effects recycling of generator 30 back to its first condition in which a pulse is again produced at output tap 1, and another counting sequence is started. Each of the 400 output taps of generator 30 therefore produces a single output pulse (.75 second in duration) for every 400 received from the fifteenth tap of pulse generator 20. Since the pulses from output tap of generator 20 occur at the rate of only one every .75 second, each of the output taps of generator 30 produces only a single pulse every five minutes.

Output tap 1 of timing pulse generator 20 is connected to one input circuit of a normally-closed gate circuit 35 Whose output circuit is connected to one input of a flip flop or bistable multivibrator 36. The output circuit of flip op 36 is in turn coupled to a relay 38. Output tap 4 of generator is connected to another input of flip flop 36 and also to respective inputs of a pair of flip ops 41 and 42. Flip flop 42 has its output circuit coupled to -another input of gate 35 to provide a gating signal therefor. Tap 400 of generator is coupled, via a differentiator and clipper 43, to another input of liip op 42. Output tap 12 of generator 20 is coupled to another input of flip flop 41. The output circuit of reset pulse generator 17 is connected to separate input circuits of voltage source 16, timing pulse generator 20, flip op 41, flip flop 42, iiip flop 36, counter 28, and timing pulse generator 30. The labels OFF and ON adjacent the input connections of the ip ops will prove beneficial when the operation of the circuitry of FIGURE 1 is subsequently explained.

A source of positive D.C. or unidirectional voltage 45 has one of its output terminals grounded and the other connected to a normally-open fixed contact 46 which is controlled by relay 38. The movable contact 47, controlled -by relay 38, is coupled through an RF or radio frequency isolating coil 48 to the center conductor of a coaxial cable 50, Whose outer conductor is grounded, which extends to every subscriber receiver in the system. Coil 48 provides a low impedance path for D.C. but a relatively high impedance path for television signals. The output of D.C. voltage source 45 is also connected to the movable contact 51 of a simple manually adjustable two-position drop-out switch 52 which is adapted to be controlled by the operator at the central office. Switch 52 is illustrated in its OFF position. In its ON position, contact 51 engages a fixed contact 53 which is coupled to the input of a monostable multivibrator 55, one output terminal of which is grounded while the other is coupled through coil 48 to the center conductor of coaxial cable 50.

Normally-closed fixed contact 57 of relay 38 is connected to one input terminal of an amplifier 61 whose other input terminal is grounded. A resistor 62, preferably of 600 ohms resistance, is also coupled across or in shunt with the input terminals of amplifier 61. The output circuit of amplifier 61 is coupled to the punch magnet 64 of motorized paper tape punch 34 and also to a light or lamp `65 which is preferably positioned adjacent the count display `of counter 28. As will be seen, illumination of lamp 65 signifies that the receiver, whose identification number is displayed at the time, is utilizing the subscription television signal.

Each of the output taps 1-399 of timing pulse generator 30 is connected to the fixed switch contact of an assigned respetcive one of a series of 399 simple OFF-ON switches 67. All 399 movable contacts of switches 67 are connected in common and to one terminal of a relay 71, the other terminal being grounded. The output circuit of flip flop 41 is also coupled to relay 71. A pair of normallyopen shorting contacts for resistor 62 and the input of amplifier 61 are controlled by relay 71. Specifically, a fixed contact 73 is grounded while a movable relay contact 74 is connected to the ungrounded terminal of resistor 62.

Block 75 designates all of the equipment and circuitry required for producing a subscription television program signal. The television signal may take the form of that which is radiated from any conventional non-subscription television transmitter in that it may be uncoded and may have an RF carrier frequency selected so that it is transmitted in one of the VHF or UHF preassigned channels. On the other hand, if desired, the television signal may -be scrambled or coded so that it has to be treated or operated on at the receiver before it may be utilized. In the present embodiment, the television signal is not coded but the carrier frequency is selected so that the television signal does not fall into any one of the conventional television channels. For example, it may occupy the portion of the frequency spectrum from 160.25 to 166.25 megacycles, which lies between VHF channels 6 and 7.

If it is desired to add the transponding equipment to a conventional television receiver, as is the case in the described embodiment, it will be seen that RF conversion circuitry will be required to heterodyne the television signal, produced by source 75, from its nonstandard channel to one of the conventional, standard channels to which the receivers tuner may respond. One output terminal of television signal source 75 is grounded, while the other is coupled through 4a condenser 76 to the center conductor of coaxial cable 50 to permit the television signal to be conveyed to all 399 receivers in the system.

The central otiice equipment of FIGURE 1 also includes a tone generator 81 which continuously produces a sinusoidal tone signal having a frequency falling in the audible range. One output terminal of generator 81 is coupled to ground while the other is connected to the movable contact 82 of a manually adjustable two-position switch 83 which is adapted to be actuated by the operator. Switch 83, as illustrated, is in its OFF position in which the output signal from generator 81 is not utilized. On the other hand, when switch 83 is adjusted to its ON position movable contact 82 engages a iixed contact 84 which is connected to a conventional telephone line 85. It is contemplated that the telephone line may be selectively connected, via conventional telephone exchange switching equipment, to any one of the subscribers in the system.

Before an explanation of the operation of the FIGURE l equipment will be presented, a structural description of the receiver apparatus of FIGURE 2 should initially be provided. An understanding of the construction of the entire system is most helpful before an operational description is in order. Accordingly, consideration will now be given to the structural details of FIGURE 2.

With the exception of a slight variation from one receiver to the next, specifically in the phasing of the timing mechanism which will be considered, each of the 399 receivers in the system may be of identical construction and for that reason FIGURE 2 adequately illustrates the construction of any given one of the receivers.

Only a single coaxial cable 50 will be required to join all 399 receivers. In other words, all of the receivers may be tied to the same coaxial cable in parallel. Of course, appropriate amplifiers may be inserted in series with the cable if and where necessary. In the receiver of FIGURE 2, the center conductor of cable 50 is coupled through a D.C. blocking condenser 8S to the input of an RF converter 90, the output of which is coupled to the front end of a conventional television receiver 92. Actually, the output of converter 90 may be connected to the antenna input terminals of receiver 92. When RF converter 90 is enabled (namely, rendered operable), in a manner to be explained, the television signal, which occupies a nonsaturated channel at the input of the converter, is heterodyned to one of the VHF or UHF channels which is not used by other television transmitters in the particular geographical area where the illustrated system is to be employed. For example, RF converter 90 may be adapted to heterodyne the incoming television signal from the nonstandard channel (16025-16625 megacycles) to channel 8 which extends from 180 to 186 megacycles.

Block 95 represents a source of A.C. line voltage available at the receiver, namely a 120 volts, y60 cycles per second A.C. power supply. Since the central office and receiver will probably both receive power ultimately from the same power generating station, sources 95 and 10 will effectively be the same. Output terminal 96 of power supply 95 is directly connected to the upper input terminal 98 of a source 99 of D.C. or unidirectional voltage and also to the right input terminal 100 of a synchronous motor 101. Output terminal 97 of voltage source 95 is connected to the movable contact 102 of a subscription television ON-OFF switch 103 which is shown in its ON position in which contact 102 engages a fixed contact 104 which is in turn connected to the movable Contact 106 of the push button actuated latching switch. Contact 106 is actuated by the subscriber depressing a push button control 105. The push button is spring biased to return to its elevated position when the subscriber removes pressure, but contact 106 latches or locks into engagement with a fixed contact 108, by means of latch 153 in a manner to be explained, to retain an electrical connection therebetween.

Fixed contact 108 is connected to the left input terminal Fil 107 of motor 101. The motor, when energized, drives a pair of movable devices or cam discs and 116 through a slip clutch 109. Cams 115 and 116 may be driven in either a continuous motion or in a step-by-step motion. An appropriate gearing arrangement is employed so that motor 101 may rotate cam disc 115 in a clockwise direction at the rate of 1/5 revolution per minute or one revolution every live minutes, while cam disc 116 is rotated, also in a clockwise direction, at the rate of four revolutions per minute or 20 revolutions in ve minutes. Motor 101, slip clutch 109, discs 115 and 116, and associated apparatus to be described, provide a timing or cycling mechanism which advances through each one of a multiplicity of different conditions or steps in time sequence. As will be seen, the relative or combination of positions of both discs 115 and 116 at any given time during the ve-minute operating cycle may be considered a single condition or position of the timing mechanism. In this way, 399 different combinations of positions of devices 115 and 116 may conveniently consitute 399 different and distinct conditions of the timing mechanism. It will be made apparent that each of the 399 conditions will be assigned to a different one of the 399 subscribers in the system. Each receiver' will be interrogated when its timing mechanism is established in its assigned condition.

As will be seen, there will be times when it is desired to arrest the rotation of movable devices or cams 115 and 116 while maintaining motor 101 energized. Slip clutch 109 is provided to permit the motor to continue rotating while the cams are held from rotating. Movable devices 115 and 116 are illustrated in what may be called their reference positions which will also be considered the reference condition of the timing mechanism. In that position, a pin element 118 which is perpendicular to and projects out from the exposed surface of disc 115, bears against the right end of a lever 120 which is pivoted at pivot point 121. The left end of lever 120 is connected to a coil spring 122 which imparts a constant clockwise bias or torque to the lever. The left end of lever 120 controls a pair of homing contacts 124, which are connected respectively to output terminal 97 of A.C. power supply 95 and to input terminal 107 of motor 101. In the reference position shown, pin 118 has efrected a slight rocking or pivoting of lever 120 in a counter clockwise direction around pivot 121 and against the tension of spring 122 suilicient to cause the left end of the lever to open homing contacts 124 and 12S. In any other position of movable device 115 that that shown in FIGURE 2, pin 118 is out of engagement with lever 120, thereby permitting the lever to pivot slightly clockwise under the tension of spring 122 to effect closing of contacts 124 and 125. Since disc 115 makes only one revolution in 5 minutes, once it leaves its reference condition shown in FIGURE 2 contacts 124iand 125 are not reopened until about 5 minutes later.

Movable device 115 has a notch 128 on its periphery which is shaped to engage the left end of an arresting lever 131 after cam 115 has rotated clockwise a predetermined angular distance from its reference position. Specifically, lever 131 is pivoted at pivot point 132 and spring 133 urges the left end of the lever against the periphery of claim 115. With this arrangement, lever 131 is provided with a normal counterclockwise bias so that it falls into notch 128 to arrest the movement of, and to hold, device 115. As illustrated, when cam 115 is advanced out of its reference position, approximately live seconds will be required before notch 128 engages arresting lever 131.

Another arresting lever 135 is urged against the periphery of movable device 116. To elucidate, lever 135 is pivoted at pivot point 136 and spring 137 provides a normal counterclockwise bias of the left end of lever 135 against the periphery of cam 116. Cam 116 is also provided with a notch 139 on its periphery which is shaped to engage arresting lever 135 a predetermined time interval after the cam has been advanced, or rotated clockwise, out of its reference position. As in the case of movable device 115, device 116 requires five seconds, once it is actuated out of its reference position, before the left end of lever 135 falls into notch 139 at which time rotation of cam 116 is arrested. Of course, the reason that disc 116 rotates or steps clockwise so much farther in tive seconds than does disc 115 is because disc 116 rotates twenty times faster than does cam 115. The positions in which devices 115 `and 116 are established when arrested will lbe called the starting position or starting condition of the timing mechanism, for reasons which will become appa-rent later.

The left end of arresting lever 135 controls a pair of contacts 142 and 143 which are connected respectively to the lower input terminal 144 of yD.C. voltage power supply `99 :and output terminal 97 of A.C. power supply 95. In the reference position shown, lever 135 holds contacts 142 and 143 open. When movable device 116 is in its starting position, at which time the left end of lever 135 Idrops into notch 139, contact 143 lowers sufficiently to engage contact 142.

For convenience of illustration, arresting levers 131 and 135 have been shown as `separate elements. In :a preferred construction of the invention, discs 115 and 116 are par* allel to each other and the functions of levers 131 and 135 :are performed by a single lever. As illustrated, actuation of either one of levers 131 and 135 is imparted to the other and to that end they are ganged or physically tied together as shown by dashed construction line 145.

Lever 135 is provided with an L shaped portion 135a which effectively serves :as a sensing arm from sensing the position of movable device 116. Disc 116 has an interposer element 146 which is perpendicular to and projects out from the exposed surface of disc 116. In the starting position of movable device 116, interposer 146 is in the position shown in dashed construction immediately to the left of, but spaced from, the `short leg of L shaped portion 135a to establish :a limit on clockwise rotation of lever 135, for reasons to be explained.

Push button control 105 also actuates another pair of latching contacts 151, 152. Specifically, contacts 151 and 152 are normally open, but when push button 105 is depressed by the subscriber movable contact 151 engages fixed contact 152 and at the same time becomes locked in the closed position by virtue of latch member 153. Contact 151 is ganged or mechanically connected to contact 106, las shown by dashed construction line 154, and thus latch 153 also serves to hold contacts 106 and 108 locked in their closed position. Latch 153 is spring biased in a clockwise direction around pivot point 154 and may "be pivoted counterclockwise t-o release both pairs of latching contacts by actuation of lever 135 in a manne-r to be explained.

When voltage source 99 is energized, it provides unidirectional voltage of -both positive D.C. and negative DC., preferably around +30 volts and -30 volts respectively the -1\D.C. output terminal of source 99 is coupled to an input of a pulse amplifier 157 and also to an input of RF converter 90 in order to energize those two circuits. The -D.C. output terminal of source 99 is connected through normally-closed relay contacts 158 and 159 and la circuit junction 197 to be described to fixed contact 152.

Telephone line 85 from the cen-tral ofiice is connected to one input of a frequency selective rectifier 161 whose other input is grounded. Unit 161 comprises a resonant circuit, which is tuned to the frequency of the signal generated by tone generator 81 in the central office, plus a rectifying circuit in order that the signal bursts from generator 81 may be selected and rectified to produce a negative polarity pulse. The output of unit 161 is coupled through an isolating diode 162 to a relay 163 which controls contacts 158 and 159. A fixed relay contact 164, which lies opposite fixed contact 159, is connected to the junction of diode 162 and relay 163. When the relay energizes, movable contact 158 opens its connection with contact 159 and engages contact 164. Relay 163 also controls a pair of normally-open contacts 166 and 167. Fixed contact 167 is connected to contact 104 of the subscription television ON-OFF switch 103 and movable contact 166 connects to input terminal 144 of D.C. voltage source 99.

Latching contact 151 connects to one terminal of a relay 171 whose other terminal is grounded. Relay 171 controls two pairs of normally open contacts. Specifically, a fixed contact 172 is connected 'to output terminal 97 of A C. line voltage source while a movable contact 173, which engages contact 172 when relay 171 is energized, connects to input terminal 144 of D.C. power supply 99. A fixed contact 174 is coupled through an RF isolating coil 175 to the center conductor of coaxial cable 50, while la movable contact 176, which is brought into engagement with contact 174 when relay 171 energizes, is connected to the anode terminal of a diode 179, the cathode terminal of which is coupled to another input of pulse amplifier 157.

The output circuit of amplifier 157 is coupled to a relay or solenoid 181 which, when energized, :actuates arresting lever 135. Specifically, relay 181 effects rocking or pivoting of lever 135 in a clockwise direction against the tension of spring 137. As mentioned previously, when device 116 is established in its starting condition, interposer 146 is adjacent but slightly spaced from sensing arm 135:1. Operation of relay 181 at that time effects clockwise pivoting of layer 135 but only to the extent determined by the spacing between interposer 146 and sensing arm 13551. This spacing separation is set so that lever 135 rocks clockwise only to a sufiicient extent to raise the left ends of levers 135 and 131 out of engagement with -notches 139 and 128, respectively. Such operation effects :a release of the anrest of movable devices and 116.

While `the clockwise pivoting of arresting lever by the energization of relay 181 is suficient to withdraw levers 135 and 131 from notches 139 and 128, interposer 146 prevents the extreme right end of leve-r 135 from engaging latch 153. On the other hand, if relay 181 is energized when movable device 116 is in :any other position but its starting position, lever 135 will pivot sufficiently clockwise to engage and pivot latch 153 counterclockwise, thereby lto release latching contacts 151 and 152, and 106 and 108.

Preferably, cams 115 and 116- are constructed of some suitable insulating material, such as plastic of some appropriate type. This permits the disposing of an electrically conductive element on the periphery of each of the two cams in order to effect the completion of a circuit when those cams reach predetermined positions after they have left their starting positions. Specifically, a metallic conductive segment 183 is clipped or mounted to the periphery of cam 115 at some point on its periphery with respect to notch 128, and a metallic conductive segment 184 is mounted or clipped on cam 116 at some polnt around its periphery with respect to notch 139. The relative or combination of positions of the two segments 183, 184 is unique to the particular receiver illustrated and indicate the one condition of the 399 conditions of the timing mechanism which has been assigned to the illustrated receiver for interrogation. In other words, every one of the 399 receivers in this system will have its corresponding conductive elements 183 and 184 at a different phase, namely placed at a different combination of points on their cams. Each of segments 183 and 184 may conveniently comprise merely a fiat metallic strip which is folded over on itself. The open end of the element may then be slipped over the edge of the cam so that it straddles the periphery. Positioning or phasing of each conductive segment may be achieved merely by moving or sliding it around the periphery until the `desired point is reached.

A pair of normally-open reply switch contacts 185, 186

engage and sense the periphery of cam disc 115 While another pair of normally-open reply switch contacts 187, 138 engage and'sense the edge of disc 116. Contacts 185 and 186 are spaced apart a distance slightly less than the length of conductive segment 183 in order that those contacts may be electrically joined by the conductive ele.- ment when movable device 115 is established at a predetermined position in its cycle. Likewise, reply contacts 187 and 188 are spaced apart a distance slightly less than the length of conductive element 184 so that those contacts may be connected together when movable device 116 has been advanced to a predetermined position. When cams 115 and 116 are established in their positions in which both sets of reply contacts are closed, it may be said that the timing mechanism has advanced to the predetermined assigned condition, unique to the given illustrated receiver, at which time the receiver is examined from the central office in a manner to be described.

Reply contact 185 is connected to the -D.C. output terminal of voltage source 99 through a resistor 191, junction 197 and contacts 158 and 159. The junction 192 of contact 185 and resistor 191 is connected to the emitter 193 of a transistor 194 of the PNP variety. Base 195 of the transistor is connected via a resistor 196 to junction 197, and collector 198 of transistor 194 is connected to junction 197 through a resistor 199. The junction 201 of base 195 and resistor 196 is connected to ground through an adjustable resistor 202. Collector 198 is coupled through a capacitor 203 to one terminal of a resistor 204, the other terminal of which is grounded. The junction of condenser 203 and resistor 204 in turn is connected to the anode terminal of a diode 205, the cathode terminal of which is connected to the same input of pulse amplifier 157 as that to which diode 179 is coupled. Reply contact 186 is directly connected to reply contact 187, and contact 188 is connected to movable relay contact 176.

In considering now an explanation of the operation of the entire system, reference .should also be made to FIG- URE 3 which shows various idealized signal waveforms which appear at different points in the circuitry of FIG- URES 1 and 2. The waveforms are given letter designations in the graphical representation of FIGURE 3 and the points in the system where found are indicated by corresponding reference letters which are encircled.

Before the receivers in the system are interrogated, an operator in the central office will manually adjust switch 12 to its position in which contacts 11 and 14 engage to connect power supply to the input of reset pulse generator 17. This effects energization of generator 17 and an appropriate reset pulse is developed for application to the reset inputs 0f voltage source 16, timing pulse generator 20, fiip flops 41, 42 and 36, counter 28 and timing pulse generator 30. This insures that all of the apparatus which is reset will start off from appropriate reference positions when the interrogation process or cycle subsequently commences.

More particularly, the three Hip-flops in source 16 are reset. Timing pulse generator 20 is reset to its fifteenth stable operating condition so that the first pulse subsequently applied to its input from voltage source 16 actuates the generator to its first stable operating condition. For convenience, the two stable operating conditions of each of ip iiops 41, 42 and 36 are designated OFF and ON. When each iiip flop is in its ON condition, the output signal of the flip flop is established at a positive potential level with respect to its A.C. axis, Whereas when the flip flop is in its OFF condition, its output signal is negative with respect to its A.C. axis. The reset pulse from generator 17 causes fiip op 41 to assume its OFF condition, flip flop 42 to assume its ON condition, and flip flop 36 to assume its OFF condition. The inputs of the iiip flop to which reset generator 17 are connected have been labeled accordingly.

The reset pulse from generator 17 is also capable of resetting counter 28 so that the count visually displayed is 000. Timing pulse generator 30 is reset by generator 17 in the same manner as timing pulse generator 20. Specifically, generator 30 is actuated by the reset pulse to its 400th stable operating condition in order that the first subsequently occurring pulse from output tap 15 of generator 20 will trigger generator 30 to its first condition.

I-t is, of course, also necessary to reset motorized paper tape punch 24. For example, the paper tape may have indicia printed along its edge or recorded in some manner which will indicate `or designate the correlation of each area with a different one of the 399 subscribers. Preliminary to effecting an interrogation, the operator will make certain lthat the very first actuation of tape advance magnet 23 will move an area of the paper tape into the punching mechanism, which area has been assigned and correlated to record use information for lreceiver No. 1 in the system.

The central office equipment is now in readiness to start the interrogation process and this may be done any time during the program interval. Moreover, the interrogation 0r scanning cycle may be repeated throughout the program interval so that a determination may be made every iive minutes of the particular ones of the -receivers that are utilizing the television signal for the program, recalling that five minutes are required to examine all 399 receivers in the system. In the preferred embodiment, interrogation will commence at the beginning of each program and will continue throughout the program interval. There are advantages in doing this. For example, repeated examining of the receivers permits charges to be based on total subscription television viewing time. It may be desired to assess a subscriber a lesser charge for a given program in the event that the subscriber decides during the program that he does not care to view the entire program. As another example, there may be programs of relatively short duration, such as a heavyweight championship fight which may last only a round or two, and thus it is desirable that the interrogation cycle start at the very beginning of the tight so that use may be accurately determined during the initial five minutes of the program. As will be seen, once a subscriber tunes in to a subscription prog-ram he cannot avoid being charged by turning his subscription television ON-OFF switch 103 to its OFF position before his receiver is interrogated.

Until it is desired to effect an interrogation of the receivers, switch 12 will remain in the position in which reset pulse generator 17 is connected to the output of power supply 10. When the program begins, television signal source produces a television signal, which occupies the nonstandard channel between 160.25 and 166.25 megacycles, for transmission to each of the 399 receivers via capacitor 76 and Coaxial cable 50. The operator will then adjust switch 12 to the position shown in FIGURE l so that A C. voltage source 10y will be coupled to voltage source 16. The instant at which switch switch 12 is so positioned is indicated by the ordinate reference line in FIGURE 3 and is designated to. The output signal of flip iiop 42 is shown by waveform G in FIGURE 3 and since reset pulse generator 17 has established that flip flop in its ON condition, at time t0 curve G is established at its positive potential level with respect to its A.C. axis.

Voltage source 10 drives voltage source 16 so that a 20 cycle per second square wave may be developed at the output of source 16 as depicted by waveform A. For convenience of explanation, the first fifteen positive half cycles or positive pulses have been numbered 1-15. Responsive to the first positive pulse of curve A, timing pulse generator 20 is triggered from its reset or fifteenth operating condition to its first condition, which in turn effects the development of a pulse at output tap 1 of generator 20 as shown by the Ifirst occurring positive pulse in waveform B. As mentioned hereinbefore, the duration of each pulse at the output taps of generator 20 will be equal to one complete cycle (.05 second) of the square wave from source 16 inasmuch as generator 20 remains in each of its stable conditions until the next positive pulse of curve A occurs.

Since generator 20 cycles through its conditions 2f-15 in response to the next succeeding fourteen positive pulses of curve A, generator 20 is not actuated to its first condition until the sixteenth pulse of curve A occurs as illustrated in waveform B. Hence, output tap 1 of generator 20 produces a pulse in response to the first pulse of curve A and also in response to every fifteenth pulse occurring thereafter.

All of the curves of FIGURE 3 are shown on a discontinuous time scale abscissa, as shown by the dashed portions of each of the waveforms, to facilitate the operational description of the invention. The waveforms embrace a five-minute time interval, namely the time required to complete one entire interrogation sequence. Since 6000 positive pulses of curve A occur during a fiveminute interval, the 6000th pulse has been numbered in that waveform representation.

Timing pulse generator 20 is not triggered to its fourth condition until the occurrence of the fourth pulse of curve A and thus the fourth pulse of curve A and every fifteenth pulse thereafter produce pulses at output tap 4 as shown by waveform C. Similarly, the twelfth output tap of generator 20' develops a pulse responsive to the twelfth pulse of waveform A and every fifteenth pulse thereafter as shown by curve D. In like fashion, the fifteenth output tap of generator 20 produces a pulse upon the occurrence of the fifteenth pulse of curve A and from then on a pulse occurs at output tap responsive to each series of fifteen successive positive pulses of curve A, as illustrated in waveform E. The time duration between the succesive pulses, or pulse separation, appearing at any one of the fifteen taps of generator is .75 second and this time measurement has'been depicted in conjunction with waveform E. Since generator 20 effectively constitutes a 15:1 divider with respect to its input pulses, 6000 positive A pulses result in 400` pulses of waveform E. In fact, the 6000th pulse of curve A results in the development of the 400th pulse of curve E. An explanation of the maner in which the single pulse of curve F is developed will be deferred.

lConsider now the first occurring pulse of curve B which is applied to normally-closed gate 35. The output signal of -flip flop 42 opens gate 35 when the potential level of the signal is positive with respect to its A.C. axis, and since that output signal as shown by waveform G is positive upon the occurrence of the first B pulse, the pulse is gated into flip fiop 36, as illustrated by the first pulse of curve H. The output signal of fiip flop 36 is shown by waveform J and since reset pulse generator 17 establishes that fiip fiop in its OFF condition, at time t0 and just prior to the occurrence of the pulse of curve H waveform I will be established at its negative potential level with respect to its A.C. axis. The first -H pulse is, however, applied to an ON input of the fiip iiop and thus in response to that pulse waveform I undergoes a positive amplitude excursion and assumes its most positive potential level. The pulses of curve C are applied to OFF inputs of fiip flops 36 and 42 and thus the fourth pulse of curve A (first occurring pulse in curve C) effects actuation of those flip flops to their OFF conditions. Waveforms I and G therefore execute negative going amplitude excursions to assume their negative potential levels with respect to their A.C. axes.

The first pulse of curve I constitutes an interrogating pulse or signal and effects energization of relay 38 which in turn causes actuation of movable contact 47 toward and into engagement with contact 46. Positive D.C. voltage source 45 is therefore connected to coaxial cable 50 by way of contacts 46 and 47 and coil 48 and a positive volttage pulse is therefore applied to the cable for simultaneous transmission to e-ach o-f the 399 receivers. Of course, relay 38 deenergizes in response to the termination of the first pulse of curve J, which results in the return of con- 14 tact 47 to the position shown in FIGURE l, and thus voltage source 45 is only connected to cable 50 during the time interval defined by the positive I pulse. Consequently, the interrogating signal transmitted to each of the receivers is also essentially represented lby the waveform of curve I and is .15 second in duration.

It is expedient rat this time to leave the operational explanation of the central ofiice equipment for the moment and consider the operation of the receiving and transponding equipment of FIGURE 2. Assume that prior to the transmission of the subscription television program signal under consideration the subscriber, to whom the equipment of FIGURE 2 has been assigned, has decided that he wishes to watch the program. To do so he is initially obliged to (l) turn his channel selector switch in his receiver 92 ot channel 8, (2) turn receiver l92` on, and (3) adjust switch 103 to its ON position as illustrated in FIG- URE 2.

Incidentally, subscription television OFFON switch 103 may be ganged to another switch (not shown) which will convert the subscribers receiving equipment to one of entirely conventional form. For example, when switch 103 is adjusted t-o its OFF position, a switch may be actuated to disconnect RF converter from the antenna input termin-als of television receiver 92 and connect their terminals to a conventional television receiving antenna. The system of the invention may also be incorporated in a CATV (community antenna television) system. In that event, an additional switch wou-ld be ganged to switch 103 in order rto couple coaxial cable 50 directly to the input of television receiver 92, thereby bypassing converter 90, when the switch 103 is turned OFF.

Even though switch 103 may be adjusted `to its ON position by the subscriber preparatory to utilizing a subscription telecast, no circuits are energized in the transponding equipment. All of the equipment in FIGURE 2 is conditioned as illustrated. The manner in which movable devices 116 and 115 are automatically established in their reference conditions, namely their positions as illustrated in FIGURE 2, will be explained later.

The subscriber must then actuate push button control 105 which in turn closes contacts 106 and 108 and also contacts 151 and 152, both pairs of contacts latching in their closed positions by means of latch member 153. The spring bias for the push button returns the button fto its elevated posiiton whe-n the subscriber removes pressure. As will be seen, locking of contacts 106 .and 151 into engagement with contacts 108 and 152 respectively initiates a series of operations which result in, among other things, the enabling of the receiver so that the television signal translated over coaxial cable 50 may be utilized in receive-r 92. Since push button 105 must be depressed by the subscriber before any subscription telecast may be Viewed, the push button effectively constitutes a control that must be actuated Lby a subscriber in a predetermined manner to effect utilization of a receiver subscription television program signal.

Of course, while the present invention is illustrated as employing only one channel for subscription television reception, it is applicable to a multichannel arrangement, namely an arrangement in which different subscription television program signals may be respectively conveyed to the subscriber receivers simultaneously over different channels. In that case, converter 90 must be adjusted differently for each of the subscription channels in order that different heterodyning signals vbe developed to the end that each of the pay TV channels may be heterodyned to chan-l nel 8. The control for converter 90, or some switch mechanically connected thereto, then constitutes a control that must be actuated by a subscriber by adjusting it to a certain position (namely one of the subscription channel position) to effect utilization of the subscription television signal carried over the selected pay TV channel.

Closing of contacts 106 and 108 comple-tes the energizing circuit for motor 101 and effects advancement of the timing mechanism out of its reference condition. Specifically, closing of contacts 106 and 108 completes a connection from output terminal 97 of A.C. power supply 95 through contacts 102 and 101tof switch 103 and to terminal 107 of motor 101. Since terminal 100' of motor 101 is directly connected to output 96 of power supply 95, the motor will start rotating which in turn effects rotation of cams 115 and 116 by way of slip clutch 109. Cam 115 must rotate clock-wise only a c-ouple degrees in order to move pin 118 out of engagement with the right end of lever 120. Spring 122 therefore causes lever 120 to rock slightly clockwise to the extent necessary to close homing `contacts 124 and 125. The purpose of the homing contacts will be made apparent later in describing the manner in which discs 115 and 116 automatically assume their reference positions at the end of a subsription program.

After a period of approximately live seconds subscquent to` the instant in which motor 101 is initially encrgized, movable device 115 will have -been rotated clockwise t-o its starting position in which the left end of arresting lever 131 falls into notch 128 to effect an arrest of movement of cam 115. At :about the same time that rotation of cam 115 is stopped, movable device 116 will have rotated clockwise to its starting position at which time the left end of lever 135 falls into land engages notch 139 to cause arresting of rotation of cam 116. The timing mechanism is thus held in its starting condition by means of arresting levers 135 and 131 and the presence of slip clutch 109 `between the cams and motor 101 allows the motor -to continue to rotate since its energizing circuit is maintained.

When the left end of lever 135 drops into notch 139, contact 143 lowers and engages contact 142, This completes a connection from output terminal 97 of line voltage source 95 to input terminal 144 of D.C. voltage source 99. Source 99 thus becomes operable to produce positive D.C. and negative D.C. voltages at its upper and lower output terminals respectively. The positive voltage is applied to both R.F. converter 90 and pulse amplifier 157 to render those circuits operable. In other words, converter 90 functions to heterodyne the incoming television signal from the nonstandard channel, which the signal occupies as translated from the central office, to channel 8. Since the Channel selector in receiver 92 is already positioned to channel 8, the received subscription television program signal is successfully utilized. In other Words, the video signal is intelligibly reproduced on the picture tube of receiver 92 and the accompanying audio is delivered to the speaker of the receiver.

Application of -|-D.C. voltage to pulse amplier 157 effectively turns that amplifier on to condition it to arnplify the interrogating signal of waveform I The -D.C. voltage from source 99 is applied, by way of normallyclosed contacts 158 and 159, to contact 152. However, since contacts 151 and 152 are electrically connected and are being held in that condition by means of latch 153, the negative D.C. voltage is extended to the ungrounded terminal of relay 171 to cause energization thereof and consequent making or closing of contacts 173 and 176 with contacts 172 and 174 respectively.

The transponding equipment of FIGURE 2 is now properly conditioned to respond to an interrogating signal from the central ofiice. Assuming that the described operational steps have all occurred in the receiving equipment of FIGURE 2 prior to the generation of the first interrogating signal of curve I, that signal will result in advancing the timing mechanism from its starting condition and through each one of its 399 different conditions. More specifically, the first interrogating pulse of curve I is applied to the input of pulse amplifier 157 by way of coaxial cable 50, coil 175, contacts 174 and 176 and isolating diode 179. An amplified version of the interrogating pulse therefore appears at the output of pulse amplifier 157 and will be of a magnitude suflicient to energize relay or solenoid 181. Arresting lever 135 is therefore pivoted slightly in a clockwise direction to with- 16 draw the left end of the lever from notch 139. Since lever 135 is mechanically connected to lever 131, pivoting of lever 135 also effects raising of the left end of lever 131 in order that lever 131 may be withdrawn from engagement with notch 128. While levers 135 and 131 are rocked to the extent necessary to release the holding action on the cams, the presence of interposer 146 adjacent arm 13511 prevents lever 135 from pivoting to the extent that its right end engages latch 153.

Inasmuch as motor 101 is continuously rotating, releasing of the arresting levers permits the motor to advance movable devices and 116 out of their starting positions. Since the duration of the interrogating pulse is only .l5 second, relay 181 is energized for only a rela.- tively short time. However, the duration is sufficient to release the arrest of discs 115 and 116 long enough so that the portion of the periphery of carn 115 immediately to the left of notch 128 will move or slide under the left end of lever 131. In this way, the periphery will cam or force the left end of lever 131 upward and, since lever 135 is mechanically connected to 131, the left end of lever 135 will be likewise moved to its uppermost position. Inasmuch as disc 115 makes only a single revolution in five minutes, which is the time required for the timing mechanism to progress through all 399 conditions, once notch 128 moves under and past the left end of lever 131 the periphery of cam 115 will effectively maintain the left end of lever 135 in its uppermost position throughout the five-minute timing cycle. This is necessary since cam 116 will make twenty revolutions during that five-minute scanning interval.

When the timing mechanism progresses to the predetermined condition assigned to the illustrated receiver for interrogation, a reply signal is generated for transmission back to the central office. To explain, at a particular instant during the five-minute cycle of the timing mechanism, cam 115 will have advanced clockwise to its position in which conductive element 183 closes reply contacts 185 and 186 while at the same time cam 116 will be in the position in which conductive segment 184 electrically joins reply contacts 187 and 188. At that time, a circuit connection will be completed from junction 197 through resistor 191, contacts 135, 183, 186, 187, 184, 188, 176 and 174, and coil to coaxial cable 50 in order that a negative polarity voltage from source 99 may be transmitted back to the central office to provide a reply signal from the particular given receiver illustrated.

The reply pulse will take the form shown by waveform K (FIGURE 3) and since the two sets of reply contacts in the illustrated receiver close at a time which is assigned to and unique to that receiver, the time interval between the first interrogating pulse of curve J and the reply signal of curve K will be of a duration unique or individual to the specific illustrated receiver to provide an indication at the central ofiice that the reply signal originated at that receiver.

In the illustrated case, cam disc 115 must rotate clockwise approximately 1A of a revolution before reply contacts and 186 are closed and this does not take place until approximately 1%, minutes after disc 115 leaves its starting position, so that the time interval between the first interrogating pulse of curve I and the negative reply pulse of curve K should be approximately a minute and a fourth- Because this timing cannot be plotted on the scale of FIGURE 3, the reply pulse K received from the first receiver interrogated is shown instead, at a time approximately one second after the first interrogating pulse of waveform I has initiated an interrogation cycle. If all receivers in the system are utilizing the subscription program, reply pulses K will be received at the central station at regular intervals of .75 second after the first reply pulse K shown in FIGURE 3, throughout the entire fiveminute interrogation cycle.

It will be noted that the reply signal of waveform K falls intermediate the time intervals between the first and second pulses of curve E. In a properly operating timing mechanism, the reply pulse will fall approximately in the center of the time interval assigned to interrogate that receiver. If it is not operating properly, the reply pulse may wanden As will be explained, circuitry is provided for actually determining whether the operation of each cycling mechanism is in step or on schedule.

It will be Iapparent that while two cam discs, two conductive segments, and two sets 'of reply contacts are shown, the invention may obviously be practiced by means of only one disc, one conductive segment and one pair of reply contacts. All that is necessary is that the single disc effectively exhibits 399 different positions and that the conductive ele-ment be capable of closing the reply contacts in only a single unique one of those positions. For commercial expediency, two discs have been shown Aas it is more convenient to provide 399 dilTerent conditions of the timing mechanism by employing 399 relative positions or combination of positions of the two discs. Moreover, three or more discs may be employed, especially in a larger system with a longer interrogation cycleeg minute scanning cycle for 800 subscribers.

Attention will now be returned to the equipment of FIGURE l in order to appreciate the manner in which the reply signal from the receiver of FIGURE 2 is utilized and recorded. The rst occurring pulse of curve 'E energizes tape advance magnet 23 to position the tape so that one of the areas devoted to recording the use information for the No. 1 subscriber will be adjacent punch magnet 64. At the same time, the first E pulse actuates counter 28 so that the number 001 is displayed to the operator, indicati-ng that the No. 1 subscriber is being interrogated during the .75 second interval between the rst two E pulses. The rst E pulse also factuates timing pulse generator 30 to its first stable operating condition so that a pulse of .75 second duration is produced at 'output tap 1 of the lgenerator. 'Ihe purpose of generator 30 will, however, be explained subsequently.

Assuming now that the receiver specilically illustrated in FIGURE 2 is the No. 1 receiver in the system (rather than receiver No. 125 which would be the case when reply contacts 18S and 186 close latter 1% minutes), the negative polarity reply pulse will occur at the time shown by curve K, namely midway between the rst and second -E pulses. Since movable relay contact 47 engages its normally-closed contact 57 at the time the K pulse occurs, that reply signal will be channeled from coaxial cable 50 and through coil 48, contacts 47 and 57 to the input of amplifier 61. Assuming that amplier 61 comprises two stages of amplification, an amplied version of the reply signal of curve K is supplied to punch magnet 64 and also to light 65 to effect punching of the paper tape in unit 24 and illumination of the lamp. The punching operation provides a permanent use record that the No. 1 receiver has been utilizing the received subscription television program signal. Energization of light 65 provides a visual indication to the operator that the subscriber who has receiver No. 1 is subscribing to the subscription program at that time.

In response to the second occurring pulse of waveform E, tape advance magnet 23 energizes and moves the paper tape so that one of the Iareas devoted to recording use information with respect to receiver No. 2 will be adjacent the punching mechanism. At the same time, counter 28 actuates so that the indicia 002 is visually displayed to the operator. If the subscriber to whom receiver No. 2 has been assigned has depressed his push button control corresponding to push button 105 and is subscribing to the program, a reply pulse will be returned from that receiver approximately .4 second after the second E pulse and will eiect energization of punch magnet 64 and lamp 65 to provide a permanent record land a visual indication that receiver No. 2 is utilizin-g the program in question. Of course, if subscriber No. 2 is not watching the pay TV program no reply signal is produced.

The remaining 397 subscribers in the system are sequentially examined during the remaining portion of the five-minute interrogation or scanning period. At the beginning of each .75 second interval assigned to interrogate a respective one of the receivers, the paper tape is advanced to a new position, the next successive number is displayed in counter 28, and use information is recorded and indicated.

Returning now to the transponding equipment of FIG- URE 2, cam completes its single revolution at the conclusion of the `five-minute interrogation period and returns to its starting position :at which instant arresting lever 131 falls into and engages notch 128 to prevent further rotation of the cam. Lowering of the left end of lever 131 falso lowers the left end of lever 135 to engage notch 139 to arrest `further movement of cam 116. Hence, at the conclusion of the five-minute cycle, cam 116 is also established in its starting position. In the absence of any additional interrogation pulses subsequent to the rst pulse of curve J, the timing mechanism in the receiver will remain in its starting condition, even though motor 101 continues to rotate since its energizing circuit is maintained via closed contacts 106 and 108 which are held in their closed condition by latch 153. The receiver also remains enabled so that the subscription telecast may be utilized. This follows since voltage source 99` remains energized through the panallel paths of contacts 172 and 173 and 142 and 143, relay 171 remaining energized by way of latched contacts 151 and 152. If desired, no additional interrogation may be made throughout the remainder of the program interval. In the present embodiment, however, it is contemplated that as soon las the 399 subscribers have been interrogated another live-minute interrogation cycle will commence immediately. In this way, if a program lasts for, say an hour, each receiver will be interrogated twelve different times.

In order to appreciate the manner in which repeated interrogation cycles occur, attention should again be directed to FIGURE l. After the last or 399th receiver has been examined, the 400th pulse of curve E is generated by timing pulse generator 20. Since timing pulse generator 30 changes operating conditions in response to each E pulse, the 400th such pulse triggers generator 30 to its 400th condition to produce a pulse at output tap 400 which in turn is differentiated and clipped in circuit y43 to provide the relatively narrow positive pulse of waveform F. This pulse is applied to an ON input of ip Hop 42 to effect 'actuation of that circuit to its ON condition in which the output signal of curve G undergoes a positive going amplitude excursion to assume its positive potential level with respect to its A.C. axis.

Since the leading edge of the 400th pulse of curve E occurs in time coincidence with the leading edge of the 6000th pulse of curve A and inasmuch as the 6000th A pulse triggers generator 20 to its fifteenth condition, the 6001st A pulse from voltage source 16 triggers generator 20 to its first condition and thus the 600lst A pulse produces a pulse at output tap 1 of generator 20 as shown by the last occurring pulse in waveform B. Since the gating signal of curve G is positive at the instant the last pulse of curve B occurs, that pulse will be gated through gate 35 and to the ON input of flip op 36 as illustrated by the last pulse of curve H. This H pulse therefore turns ip flop 36 ON to initiate another interrogating pulse as shown by the last pulse of curve J. In response to the third successive positive A pulse occurring thereafter, generator 20 finds itself in its fourth condition at which time a pulse is produced at output tap 4 (as shown by the last pulse of waveform C) for application to one of the OFF inuts of flip flop 36 to return the flop op to its OFF condition thereby terminating the last J pulse.

The last occurring interrogating pulse of curve J energizes relay 38 to transmit a corresponding interrogating pulse to all receivers to initiate sequential interrogation in exactly the same manner as previously described in response to the rst J pulse. The use recording and indicating equipment in FIGURE 1 also operates in step with the interrogating sequence. In other words, the 400th E pulse changes the visual count display of counter 28 from 399 to 000. In this way, the 401st E pulse (not shown) actuates counter 28 to its 001 visual count indication. The 6000th A pulse and the 400th E pulse, with respect to generator 20, counter 28, generator 30 and flip flop 42, have the same effect as a pulse from reset pulse generator 17 so that the conditions at time t0 are re-established. With this arrangement, the 401st E pulse (not shown) effectively corresponds to the first occurring pulse of waveform E. Of course, the paper tape in unit 24 must be appropriately indexed so that each individual take area is properly correlated with the particular one of the 399 receivers which is being interrogated during the .75 second interval in which each tape area is adjacent the punching or recording mechanism.

In describing the operation of the timing mechanism of FIGURE 2, the assumption was made that push buttion 105 had been depressed by the subscriber, cams 115 and 116 had advanced to their starting conditions, and pulse amplifier 157 and converter 90 were fully enabled or energized prior to the occurrence of the rst interrogating signal of curve I. Assume now that the subscriber did not tune into the subscription program until some time after it had started. In that case, the timespaced interrogating signals (and there will Vonly be one every five minutes) that occur before pulse amplifier 157 is supplied with positive D.C. voltage will have no effect on the receiving equipment. After pulse amplifier 157 is made operable, however, the next occurring interrogating signal will be effective to release the timing mechanism from its starting condition. In this way, no matter when a subscriber subscribes to a particular program, his receiver will not be sensed until it is properly conditioned to respond and, moreover, to respond at the right time.

To elucidate, one of the salient features of the invention resides in advancing the cycling mechanism or timing mechanism from its reference condition, shown in FIGURE 2, to its starting condition in response to the actuation of control 105 in a predetermined manner, namely to its depressed position. Until these steps have been completed, the receiving equipment is not capable of being interrogated. By the time the timing mechanism has Ireached its starting condition, motor 101 is running smoothly. Hence, the cycling mechanism, once actuated out of its starting condition, steps through each one of its 399 positions in accordance with a predetermined schedule which may be Irelatively easily adhered to since the operating speed of the motor is stabilized. In this way, reliable operation of each of the 399 timing mechanisms in the system is reasonably insured in that each will experience no difficulty in advancing through its different operating steps in time sequence and in accordance with the very same schedule.

Contrast the present arrangement with an interrogat ing system in which a motor, which drives a timing mechanism, is not even energized until the `occurrence of an interrogating pulse. Because of the starting variations of most synchronous motors, especially of the relatively inexpensive type that would probably be preferred in a subscription television receiver, the operation of the timing mechanism would be far from reliable. To explain, once a motor is energized the time interval required for the motor to settle down or stabilize to a constant speed is subject to wide variations. A given motor is subject to requiring different stabilizing intervals at different times and, of course, all of the motors in a system may exhibit different stabilizing intervals at the same time. Conseqeuntly, the various timing mechanisms are susceptible of being substantially out of step, with the result that the timing of the reply signals would not accurately indicate the particular receivers tuned to a given subscription program.

It will be noted that When a receiver is utilizing a subscription telecast, the transponding equipment which is interrogated is effectively attached to coaxial cable 50. Specifically, contacts 174 and 176 are closed by relay 171 so that an interrogating signal may be conveyed from the central office to relay 181- and a reply signal may be transmitted back to the central office. One of the features of the invention resides in providing for remote actuation of all receivers at the conclusion of a program interval in order that the receivers may be disassociated from cable 50, at least with respect to the interrogating and reply signals. This may be achieved by the central station operator by positioning drop-off switch 52 to its closed position in which contacts 51 and 53 engage, thereby to apply positive D.C. voltage from source 45 to the input of monostable multivibrator 53. Being of the monostable type, the multivibrator in response to positive voltage actuates from its normal to its abnormal condition in which it remains for a predetermined interval at the termination of which the multivibrator returns to its normal condition. The multivibrator is constructed so that a pulse of positive polarity is produced at its output while the circuit is established in its abnormal condition to provide a drop-off or drop-out signal which is conveyed to each receiver via coil 48 and coaxial cable 50. The dropolf pulse is consequently translated to relay 181 in the same manner as is each interrogating pulse. Monostable multivibrator 55 is so constructed that the duration of the positive drop-off pulse, namely the interval in which the multivibrator is established in its normal condition, will be of sufficient duration to energize relay 181.

If the operator closes switch 52 at some instant during a five-minute interrogating cycle when cam disc 116 is not in its starting condition (and it will be in its starting position twenty different times during the five-minute interval), actuation of relay 181 effects pivoting of arresting lever 135 in a clockwise direction a distance sufficient for the right end of lever 135 to engage, and pivot counterclockwise, latch member 153. Such movement of lever 135 is permitted since interposer 146 will be. at some position other than its effective limiting position shown in dashed construction. Counterclockwise pivoting of latch 153 releases both contacts 106 and 151, permitting those contacts to spring back to their open positions illustrated in FIGURE 2.

Opening of contacts 151 and 152 effects de-energization of relay 171 which in turn opens contacts 172 and 173 and also contacts 174 and 176. Opening of contacts 106 and 108 opens one parallel energizing circuit connection for motor 101 but since disc 115 will be at some inter- -mediate step in its five-minute operating cycle, homing contacts 124 and 125 will be closed to permit the motor to remain energized. Hence, cams and 116 continue to rotate until they reach their respective reference positions shown in FIGURE 2 at which instant pin 118 pivots lever counterclockwise to open homing contacts 124 and 125. This de-energizes motor 101 and thus it stops rotating and cams 115 and 116 also stop rotating. In the reference condition of the timing mechanism, shown in FIGURE 2, contacts 142 and 143 are open so there is no energizing circuit for D.C. voltage source 99. Absence of D C. voltage from source 99 renders both pulse amplifier 157 and RF converter 90 inoperative so that the use indieating means as Well as the receiver are both disabled.

One important advantage in remotely disconnecting the receivers at the termination of a subscription program is that prior to subscribing to a subsequent program the subscriber must perform a positive act. Specifically, he must actuate push button control 105. In this way, if a subscriber utilizes or watches one program he will not be charged for the subsequent program, unless of course he wishes to subscribe to it, in the event that the subscriber inadvertently failed to turn his subscription television OFF-ON switch 103 to its OFF position at the conclusion of the first program. However, with applicants feature of requiring a specific manipulation by the subscriber before a subsequent program is utilized, he will not be charged unfairly for programs to which he did not actually wish to subscribe.

It will be noted that once a receiver is enabled, switch 103 is bypassed and a five-minute interrogation cycle will be followed even though the subscriber turns switch 103 off. Once the cycle commences, switch 103 is not needed since the energizing circuit for the motor will be completed through homing contacts 124 and 125. With this arrangement, a subscriber cannot avoid being charged for a given program by tuning in to that program and then turning switch 103 off just prior to the instant in the five-minute scanning cycle in which his receiver is interrogated.

While the vreliability of the present system represents a significant improvement over prior interrogating systems, on rare occasions a given one of the timing mechanisms in the system may conceivably become faulty and fail to operate in step with the timing mechanisms in the other receivers and in step with the cycling apparatus at the central oliice, namely voltage source 16, timing pulse generator 20, motorized paper tape punch 24, and magnetic impulse counter 28. Obviously, if the timing mechanism in a particular receiver is faulty and does not progress through its multiplicity of different conditions in synchronism with the operationl of the cycling apparatus at the central ofiice, a reply signal may be generated in some time interval other than the specific .75 second interval in the five-minute cycle allotted for the faulty timing mechanism to respond. This would, of course, result in the indication and recording of incorrect use information. Not only would the subscriber with the malfunctioning timing mechanism avoid the recording of a charge assessment for a given program, but there is a possibility that a charge assessment will be made to a subscriber who did not even subscribe to the given program. For this reason, it is desirable to provide some means for determining whether the operation of each timing mechanism is adhering to a predetermined schedule. In accordance with another feature of the invention, if any timing mechanism is out of step, the receiver associated therewith is effectively disabled and the transponding equipment interrogated is dropped ofi of the coaxial cable.

To explain, at time t flip flop 41 is established in its OFF condition as a result of the reset operation effected by reset pulse generator 1 7 and thus the output signal of fiip Hop 41 is at its negative potential level with respect to its A.C. axis at that time, as shown in curve L. The first occurring pulse of curve D is produced from the twelfth pulse of curve A and is appiled to the ON input of iiip op 41 to trigger the fiip fiop to its `ON condition. Hence, waveform L undergoes a positive -amplitude excursion since the output signal of flip flop 41 assumes its most positive level in response to the vfirst D pulse. Flip flop 41 remains in its ON condition until the occurrence of the next pu-lse at output tap 4 of generator 20 which pulse is the second occurring one in waveform C. Since that C pulse is applied to an OFF input of flip flop 41, the flip flop is triggered at that time and thus the output signal -of curve L assumes its most negative potential level. The next pulse which occurs -at output tap 12 of generator 20, namely the second pulse of curve D, triggers flip op 41 to its ON condition yas shown in waveform L. The next occurring pulse at output 4 (not specifically shown in 'FIGURE 3) returns waveform L to its negative potential level. v f

By comparing waveforms E and L, it will be noted each negative polarity pulse yof curve L lies midway between a pair of successive E pulses. Moreover, by comparing the single reply pulse illustrated in curve K with the first occurring negative pulse of curve L it will be seen that the K pulse is of shorter duration than and falls approximately in the middle of the first negative L pulse. As mentioned previously, in a properly operating timing Cil -mechanism the reply pulse will occur approximately in the middle ofthe .75 second interval between the adjacent E pulses which is assigned to that timing mechanism. The duration and timing of each negative L pulse defines the permissible limits within which va reply pulse may Wander before the timing mechanism is considered to be out of step. In other words, if the reply pulse falls anywhere within the interval defined lby a concurrent negative L pulse, a correct use recording will still be effec-ted in the central office. However, it will be shown that in the event a reply pulse from an out-of-step timing mechanism becomes out of phase with the L signal and wanders into a positive pulse interval of that signal, a determination is automatically made that the timing mechanism in question is functioning out of synchronism and that timing mechanism will be disconnected from the coaxial cable.

More particularly, the sign-al of waveform L is applied lto relay 71 which energizes in response to each positive pulse of that signal. Inso doing, shorting contacts 74 and 73 close thereby grounding the upper terminal of resistor 62. Resistor 62 and the input of amplifier 61 therefore become shorted out during the intervals in which relay 71 is energized, namely during the positive pulse intervals of curve L.

To fully appreciate the manner in which 4an out-of-step receiver may be remotely and selectively disconnected without affecting any of the other receivers in the system, certain portions of both the FIGURE l and FIGURE 2 circuitry have been redrawn in FIGURE 4. `During the entire five-minute reply time, relay 38 is de-energized and contacts 47 and 57 make. The impedance of the central office between the center conductor of coaxial cable 50 and ground will therefore be primarily that which is presented by -resistor 62. This is especially true when that resistor is given a value around 600 ohms and the input of amplifier 61 is of a considerably greater resistance. Hence, the impedance presented to a reply signal is accurately shown in FIGURE 4. Of course, RF coils 4S and have been ignored since they add negligible impedance to the signal in question and are only provided to Iblock or isolate the `much higher frequency television signa'l from the interrogating and interrogated equipment.

The resistance of the center conductor of coaxial cable 50 will be signicant however and, of course, this will vary with the length of the cable. The line resistance of the cable has therefore been shown in FIGURE 4 and is interposed between the ungrounded termin-al of resistor 62 and reply contact 188. Since only the negative D.C. volt-age from source 99 is of interest, that source has been yschematically shown in FIGURE 4 merely by a battery whose positive terminal is grounded and whose negative terminal is connected through contacts 158 and 159 of relay 163 to junction 197.

The components shown in FIGURE 4 form a bridge circuit which may be analyzed in terms of c-onventional bridge circuit theory. The relative values of the resistances 'are selected so that the fol-lowing conditions are met. Resistor 202 has a resistance approximately twice that of resistor 196. Assuming that the negative D.C. voltage at junction 197 is -30 volts, the potential at junction 201 will therefore be 20 volts. With both sets of reply contacts and the shorting contacts open, junction 192 will, of course, :be established at -30 volts. Since transistor 194 is of the PNP type, it will not conduct at this time since its base 195 will be positive (-20 volts) with respect to its emitter 193, which will be established at -30 volts.

With both pairs of reply contacts closed but with the shorting contacts open, the -30 volts D.C. 'at junction 197 will `be dropped across the series circuit including resistor 191, the line resistance of cable 50, and resistor 62. The relative values of these resistances will be such that junction 192 will be established at approximately 21 volts. Transistor 194 will still not be forward biased at this time, however, since its base being established `at -20 volts is still positive with respect to emitter 193.

Hence, when a receiver replies at -the correct time, transistor 194 is not turned on.

However, if the shorting contacts are closed at the same time both sets of reply contacts are also closed, resistor 62 is shorted out. The voltage drop across resistor 191 therefore increases, raising the potential at junction 192 in a positive direction. Specifically, the potential at that junction will be approximately -19 volts and this change is sufiicient to render transistor 194 conductive since its base-emitter junction will now be forward biased. Emitter-collector current therefore ows through resistor 199 thereby developing a positive going pulse at collector 198 for application through capacitor 203 and isolating diode 205 to the input of pulse amplifier 157. Relay 181 thereupon receives an energizing pulse from amplifier 157 causing the timing mechanism to be dropped off the cable and the receiver to be disabled.

Hence, if any timing mechanism is out of sync its reply contacts will be closed during the occurrence of a positive pulse of waveform L at which time shorting contacts 73, 74 are closed at the central office and this in turn disables the receiver and the use indicating means at that receiver. Disabling the use indicating apparatus prevents the transmission of subsequent reply signals to the central office which is desirable since those signals occur at the wrong time and thus may result in a recording of a charge to the wrong subscriber. Disabling the receiver so that the program no longer can be enjoyed provides notice to the subscriber that his equipment is malfunctioning. While it is true that he may then depress his push button control 105 to relatch contacts 106 and 108 and 151 and 152, a time interval of up to five minutes will be required (depending on where in the interrogation period the reply contacts close) before both cams 115 and 116 will be in their respective starting positions in which the left end of lever 135 drops into notch 139 to effect closing of contacts 142 and 143 thereby to energize voltage source 99 which, of course, is necessary before RF converter 90 will be rendered operable.

It is contemplated that upon being apprised of the faulty condition of his equipment, the subscriber will telephone the subscription television central office, through conventional telephone exchange apparatus, and will apprise the subscription television operator of the faulty condition. The operator may then dispatch a service man to the home of that subscriber so that the malfunctioning equipment may be either repaired or replaced. In the meantime, however, it is desirable to provide some means, which may be remotely controlled from the central oice, for re-enabling the receiver so that the subscribed may view the remainder of the program. This may be achieved -by the operator by closing switch 83 so that a tone signal from generator 81 may be conveyed to the calling subscribers equipment over telephone line 85 which represents the telephone circuit which extends through the telephone exchange and connects the subscription television operator to the home of the calling subscriber.

The tone burst is detected and rectified by frequency selective rectifier unit 161 to produce a negative polarity pulse for application through isolating diode 162 to relay 163 to effect energization thereof. Contact 158 breaks its normal connection with contact 159 and engages contact 164 while contacts 166 and 167 electrically connect. An energizing circuit for voltage source 99 is thus completed from output terminal 97 of source 95 in via contacts 102, 104, 167 and 166 to input terminal 144 of voltage source 99. Positive DJC. is thus again developed for application to converter 9() to reenable the receiver to utilize the subscription television program signal. Closed contacts 158 p and 164 apply -D.C. to relay 163 to maintain the relay energized. Switch 83 may then be opened by the operator and the telephone connection may be disconnected. Opening of contacts 158 and 159 insures, among other things,

fil

that no reply signals will be generated in and transmitted from the faulty equipment.

At the conclusion of the program interval, the subscriber may effect de-energization of relay 163 merely by operating the OFF-ON switch 103 to its OFF position, thereby breaking the energization circuit for voltage source 99 which in turn removes negative D.C. voltage from the relay.

There may be times when it is desirable to selectively disable a given receiver for other reasons than malfunctioning of the timing mechanism in the receiver. For example, if a subscriber is delinquent in paying his subscription television bill for the charges previously recorded, it may be desired to render his receiver disabled without actually sending a service man to the home of the delinquent subscriber. This may be done by means of timing pulse generator 30.

Assuming that subscriber No. 3 is delinquent and it is desired to disable his receiver, switch 67 which is connected to output tap 3 of generator 30 will be closed by the operator. At the beginning of the .75 second interval devoted to interrogating subscriber No. 3, generator 30 will be actuated to its 3rd operating condition by a pulse of waveform E to produce a pulse at output tap 3. Generator 30 remains in its 3rd condition throughout the .75 second interval. Hence, the pulse at output tap 3 will be .75 second in duration and completely coincides with the interval in which subscriber No. 3 is interrogated. Relay 71 energizes in response to that pulse from tap 3 to cause shorting contacts 73 and 74 to close. When both sets of reply contacts at the No. 3 receiver close the shorting contacts will also be closed and, as explained hereinbefore in connection with lFIGURE 4, the transistor 194 in that receiver will be rendered conductive to produce a pulse for application through pulse amplifier 157 to relay 181 in order to disable the subscribers equipment.

While the invention has been illustrated as being applied to a closed circuit television system, the television signal may be transmitted to each receiver over the air rather than through a coaxial cable. Moreover, the interrogating and reply signals may be transmitted between the central otiice and the receivers by way of air-borne transmission. Furthermore, it is obviously not necessary that the interrogating and reply signals employ -the same vehicle as the television signal. For example, the television signal may be conveyed to each receiver via air-borne transmission or a coaxial cable while at the same time the interrogating and reply signals may use a completely separate conductive connection such as a simple two conductor line or twisted pair such as is used for telephone connections.

Furthermore, while pulses of D.C. have been used in the illustrated embodiment of the inviention to provide the time-spaced interrogating signals, bursts of a sinusoidal signal or some alternating signal may be used instead. Moreover, sinusoidal bursts, such as audio tones, may be employed for the reply signals rather than pulses of D.C. as described herein. The use of audio tones is particularly attractive when the invention is applied to a multi-channel system in which two or more different subscription television channels are employed. In this case, audio tones of different frequencies may be used to indicate to the central oiiice the particular one of the subscription channels which is being used by a subscriber.

The invention provides, therefore, a novel system for sequentially interrogating a plurality of subscription television receivers from a central ofiice to determine the particular receivers which have been tuned to reproduce a subscription television program signal. Each receiver includes a timing mechanism which advances, when the receiver is adjusted to utilize the program signal and in response to an interrogating signal received from the central ofiice, from a starting condition and through each one of a series of different conditions in time sequence. When the timing mechanism at each receiver reaches a preassigned condition, unique to the receiver, a reply signal iS transmitted back to the central ofiice with a time separation from the interrogating signal which is unique to the receiver.

While a particular embodiment of the invention has been shown and described, modifications may be made, and it is intended in the appended claims to cover all such modifications as may fall within the true spirit Iand scope of the invention.

We claim:

1. In an interrogating system for sequentially examining in response to an interrogating signal transmitted from a central office a plurality of subscription television receivers, each of which includes a control that must be actuated by a subscriber in a predetermined manner to eiect -utilization of a received subscription television program signal, to determine the particular ones of said receivers that have been so actuated, each given one -of said subscription television receivers comprising:

a timing mechanism adapted to be advanced from a reference condition to a starting condition and then to and through each one of a multiplicity of different conditions in time sequence;

means responsive to such actuation of said control in said given receiver for advancing said timing mechanism from its reference condition to its starting condition and for holding said mechanism in its starting condition;

means responsivefto said interrogating signal for adfvancing said timing mechanism from its starting condition and through each one of at least some of its multiplicity of different conditions;

and means operable when said timing mechanism subsequently reaches a predetermined condition, which condition is unique to said given receiver, for transmitting a reply signal back to said central office, the time interval between said interrogating signal and said reply signal thereby being of a duration unique to said given receiver to indicate at said central oilice that said reply signal originated at said given receiver.

2. In an interrogating system for sequentially examining in response to an interrogatin g signal transmitted from a central office a plurality of subscription television receivers, each of which includes a control that must be actuated by a subscriber in a predetermined manner to effect utilization of a received subscription television program signal, to determine the particular ones of said receivers that |have been actuated, each given one of said subscription television receivers comprising:

a cycling mechanism which progresses from a starting condition to and through each one of a multiplicity of different conditions in time sequence in completing a cycle of operation;

-means responsive to such actuation of said control in said given receiver for advancing said cycling mechanism from a reference condition to its starting condition and for holding said mechanism in its starting condition;

means responsive to said interrogating signal for advancing said cycling mechanism from its starting condition and through each one of at least some of its multiplicity of different conditions;

and means operable when said cycling mechanism subsequently reaches a predetermined condition in its cycle, w'hich condition is unique to said given receiver, for transmitting a reply signal back to said central oflice, the time interval between said interrogating signal and said reply signal thereby being of a duration unique to said given receiver to indicate at said central oliice that said reply signal originated at said given receiver.

3. In an interrogating system for sequentially examining in response to time-spaced interrogating signals transmitted from a central oiiice a plurality of subscription television receivers, each of which includes a control that must be actuated by a subscriber in la predetermined manner to effect utilization of a received subscription television program signal, to determine the particular ones of said receivers that have been so actuated, each given one of said subscription television receivers comprising:

a timing mechanism adapted to be advanced from a reference condition to a starting condition and then to and through each one of a multiplicity of different conditions in time sequence;

means responsive to such actuation of said control in said given receiver -for advancing said timing mechanism from its reference condition to its starting condition and for holding said mechanism in its starting condition;

means responsive to one of said interrograting signals occurring after said timing mechanism has been established in its starting condition for advancing said timing mechanism from its starting condition and through each one of at least some of its multiplicity of different conditions;

and means operable when said timing mechanism subsequently reaches a predetermined condition, which condition is unique to said given receiver, for transmitting a reply signal back to said central otlice, the time interval between said one interrogating signal and said reply signal thereby being of a duration unique to said given receiver to indicate at said central office that said reply signal originated at said given receiver.

4. In an interrogating system for sequentially examining from a central oiiice a plurality of subscription television receivers in response to an interrogating signal transmitted from said central ofiice to said receivers over a common electrically conductive connection, each of said receivers including a control that must be actuated by a subscriber in a predetermined manner to effect utilization of a received subscription television program signal, to determine the particular ones of said receivers that have been so actuated, each given one of said subscription television receivers comprising:

a timing mechanism adapted to be advanced from a reference condition to a starting condition and then to and through each one of a multiplicity of different conditions in time sequence;

means responsive to such actuation of said control in said given receiver for advancing said timing mechanism from its reference condition to its starting condition and for holding said mechanism in its starting condition;

means responsive to said interrogating signal for advancing said timing mechanism from its starting condition and through each one of at least some of its multiplicity of diierent conditions;

and means operable when said timing mechanism subsequently reaches a predetermined condition, which condition is unique to said given receiver, for transmitting a reply signal back to said central o'ice over said conductive connection, the time interval between said interrogating signal and said reply signal thereby being of a duration unique to said given receiver to indicate at said central oice that said reply signal originated at said given receiver.

5. In an interrogating system for sequentially examining in response to an interrogating signal transmitted from a central oice a plurality of subscription television receivers, each of which includes a control that must be actuated by a subscriber in a predetermined manner to effect utilization of a received subscription television program signal, to determine the particular ones of said receivers that have been so actuated, each given one of said subscription television receivers comprising:

a cycling mechanism which progresses from a starting step to and through each one of a multiplicity of different steps intime sequence in completing each cycle of operation;

driving means operable responsive to such actuation of said control in said given receiver for advancing said cycling mechanism from a reference condition to its starting step;

arresting means for holding said cycling mechanism in its starting step, while permitting said driving means to remain operable;

means responsive to said interrogating signal for releasing said arresting means thereby to permit said driving means to advance said cycling mechanism from its starting step and through each one of at least some of its multiplicity of different steps;

and means operable when said cycling mechanism subsequently reaches a predetermined step in its cycle, which step is unique to said given receiver, for transmitting a reply signal back to said central oflice, the time interval between said interrogating signal and said reply signal thereby being of a duration unique to said given receiver to indicate at said central office that said reply signal originated at said given receiver.

6. In an interrogating system for sequentially examining in response to an interrogating signal transmitted from a central oflce a plurality of subscription television receivers, each of which includes a lcontrol that must be actuated by a subscriber in a predetermined manner to effect utilization of a received subscription televisionvprogram signal, to determine the particular ones of said receivers that have been so actuated, each given one of said subscription television receivers comprising:

a timing mechanism adapted to be advanced from a reference condition to a starting condition and then to and through each one of a multiplicity of different conditions in time sequence;

means responsive to such actuation of said control in said given receiver for advancing said timing mechanism from its reference condition to its starting condition and for holding said mechanism in its starting condition;

signal translating means, rendered operable in response to the establishment of said timing mechanism in its starting condition, for translating said interrogating signal;

means coupled to the output of said signal translating means and responsive to said interrogating signal for advancing said timing mechanism from its starting condition and through each one of at least some of its multiplicity of different conditions;

and means operable when said timing mechanism subsequently reaches a predetermined condition, which condition is unique to said given receiver, for transmitting a reply signal back to said central otice, the time interval between said interrogating signal and said reply signal thereby being of a duration unique to said given receiver to indicate at said central office that said reply signal originated at said given receiver.

7. In an interrogating system for sequentially examining in response to an interrogating signal transmitted from a central office a plurality of subscription television receivers, each of which includes a control that must be actuated by a subscriber in a predetermined manner to effect utilization of a received subscription television program signal, to deter-mine the particular ones of said receivers that have been so actuated, each given one of said subscription television receivers comprising:

a timing mechanism adapted to be advanced from a reference condition to a starting condition and then to and through each one of a multiplicity of different conditions in time sequence;

means responsive to such actuation of said control in said given receiver for advancing said timing mechanism from its reference condition to its starting condition and for holding said mechanism in its starting condition;

a unidirectional voltage power supply rendered operable in response to the establishment of said timing mech- -anism in its starting condition;

a pulse amplifier, energized by said power supply, for

amplifying said interrogating signal;

means responsive to said amplified interrogating signal for advancing said timing mechanism from its starting condition and through each one of at least some of its multiplicity of dierent conditions;

and means operable when said timing mechanism subsequently reaches a predetermined condition, which condition is unique to said given receiver, for transmitting a reply signal back to said central oflice, the time interval between said interrogating signal and said reply signal thereby being of a duration unique to said given receiver to indicate at said central oice that said reply signal originated at said given receiver.

8. In an interrogating system for sequentially examining in response to an interrogating signal transmitted from a central office a plurality of subscription television receivers, each of which incldues a control that must be actuated by a subscriber in a predetermined manner to effect utilization of a received subscription television program signal, to determine the particular ones of said receivers that have been so actuated, each given one of said subscription television receivers comprising:

a timing mechanism adapted to be advanced from a reference condition to a starting condition and then to and through each one of a multiplicity of different conditions in time sequence;

means responsive to such actuation of said control in said given receiver for advancing said timing mechanism from its reference condition to its starting condition and for holding said mechanism in its starting condition;

means controlled by said timing mechanism for enabling said given receiver to utilize said subscription television program signal;

means responsive to said interrogating signal for advancing said timing mechanism from its starting condition and through each one of at least some of its multiplicity of different conditions;

and means operable when said timing mechanism subsequently reaches a predetermined condition, which condition is unique to said given receiver, for transmitting a reply signal back to said central oliice, the time interval between said interrogating signal and said reply signal thereby being of a duration unique to said given receiver to indicate at said central oilce that said reply signal originated at said given receiver.

9. In an interrogating system for sequentially examining in response to an interrogating signal transmitted from a central oice a plurality of subscription television receivers, each of which includes a control that must be actuated by a subscriber in a predetermined manner to effect utilization of a received subscription television program signal, to determine the particular ones of said receivers that have been so actuated, each given one of said subscription television receivers comprising:

a timing mechanism adapted to be advanced from a reference condition to a starting condition and then to and through each one of a multiplicity of different conditions in time sequence;

means responsive to such actuation of said control in said given receiver for advancing said timing mechanism from its reference condition to its starting condition and for holding said mechanism in its starting condition;

television signal translating means, enabled in response to the establishment of said timing mechanism in its starting condition, for translating said received subscription television program signal to permit utilization thereof;

means responsive to said interrogating signal for advancing said timing mechanism from its starting condition and through each one of at least some of its multiplicity of different conditions;

and means operable when said timing mechanism subsequently reaches a predetermined condition, which condition is unique to said given receiver, for transmitting a reply signal back to said central office, the time interval between said interrogating signal and said reply receiver to indicate at said central oice that said reply signal originated at said given receiver.

10. In an interrogating system for sequentially examining in response to an interrogating signal transmitted from a central oice a plurality of subscription television receivers, each of which includes a control that must be actuated by a subscriber in a predetermined manner to effect utilization of a received subscription television program signal, to determine the particular ones of said receivers that have been so actuated, each given one of said subscription television receivers comprising:

a timing mechanism adapted to be advanced from a reference condition to a starting condition and then to and through each one of a multiplicity of diiferent conditions in time sequence;

means responsive `to such actuation of said control in said given receiver for advancing said timing mechanism from its reference condition to its starting condition and for holding said mechanism in its starting condition;

a unidirectional voltage power supply rendered operable in response to the establishment of said timing mechanism in its starting condition;

means responsive to said intenrogating signal for advancing said timing mechanism from its starting condition and through each one of at least some of its multiplicity of different conditions;

and means coupled to the output of said unidirectional voltage power supply and operable when said timing mechanism subsequently reaches a predetermined condition, which condition is unique to said receiver, for transmitting a reply signal back to said central oice, the time interval between said interrogating signal and said reply signal thereby being of a duration unique to said given receiver to indicate at said central ofce that said reply signal originated at said given receiver.

11. In an interrogating system for sequentially examining in response to time-spaced interrogating signals transmitted from a central oice a plurality of subscription television receivers, each of which includes a control that must be actuated by a subscriber in a predetermined manner -to elfect utilization of a received subscription television program signal, to determine the particular ones of said receivers that have been so actuated, each given one of said subscription television receivers comprising:

a timing mechanism including driving means and a movable device which is coupled to and adapted to be driven by said driving means from a reference position to a starting position and then to and through each one of a multiplicity of different positions in time sequence;

means responsive to such actuation of said control in said given receiver for maintaining said driving means operable to effect advancement of said movable device from its reference position;

arresting means for arresting the movement of said movable device when said device reaches its starting position, while permitting said driving means to remain operable;

means responsive to one of said interrogating signals occurring after said movable device attains its starting position for releasing said arresting means thereby to permit said driving means to advance said movable device from its starting position and through each one of at least some of its multiplicity of different positions,

and means operable when said movable device subsequently reaches a predetermined position, unique to said given receiver, for transmitting a reply signal back to said central oce, the time interval between said one interrogating signal and said reply signal thereby being of a duration unique to said given receiver to indicate at said central otlice that said reply signal originated at said given receiver. 12. In an interrogating system for sequentially examining in response to time-spaced -interrogating Signals transmitted from a central office a plurality of subscription television receivers, each of which includes a control that must be actuated by a subscriber in la predetermined manner to effect utilization of a received subscription television program signal, to determine the particular ones of said receivers that have been so actuated, each given one of said subscription television receivers comprising: a timing mechanism including -a motor and a rotatable cam which is coupled to and adapted to be rotated by said motor from a reference position to a starting position and then to and through each one of a multiplicity of different positions in time sequence;

means responsive to such actuation of said control in said given receiver for maintaining said motor energized to eifect rotation of said cam from its reference position; arresting means for arresting the rotation of said cam when said cam reaches its starting position, while permitting said motor to remain energized;

means responsive to one of said interrogating signals occurring -after said cam attains its starting position for releasing said arresting means thereby to permit said motor to advance said cam from itsstarting position and through each one of at least some of its multiplicity of ditferent positions;

and means operable when said cam subsequently reaches a predetermined position, unique to said given receiver, for transmitting a reply signal back to said central oHce, the time interval between said one interrogating signal and said reply signal thereby being of a duration unique to said given receiver to indicate at said central office that said reply signal originated at said given receiver.

13. In an interrogating system for sequentially examining in response to time-spaced interrogating signals transmitted from a central oice a plurality of subscription television receivers, each of which includes a control that must be actuated by a subscriber in a predetermined manner to effect utilization of a received subscription television program signal to determine the particular ones of said receivers that have been so actuated, each given one of said subscription television receivers comprising: fa timing mechanism including a motor land a movable device which is coupled to and adapted to be driven by said motor from a reference position to a starting position and then to and through each one of a multiplicity of different positions in time sequence;

means 4responsive to such actuation of said control in said given receiver for maintaining said motor energized to effect -advancement of said movable device from its reference position;

arresting means for arresting the movement of said movable device when said device reaches its starting position, while permitting said motor to remain energized;

means responsive to one of said interrogating signals occurring 4after said movable device attains its starting position for releasing said arresting means thereby to permit said motor to advance said movable device from its starting position and through each one of at least some of its multiplicity of different positions;

reply signal generating means;

means coupled to said movable device for rendering said generating means operable when said movable device reaches a predetermined position, unique to said given receiver, to produce a reply signal, the time interval between said one interrogating signal and said reply signal thereby being of a duration unique to said given receiver;

and means for transmitting said reply signal back to said central oice.

14. In an interrogating system for sequentially examining in response to time-spaced interrogating signals transmitted from a central oice a plurality of subscription television receivers, each of which includes a control that must be actuated by a subscriber in a predetermined manner to effect utilization of a received subscription television program signal, to determine the particular ones of said receivers that have been so actuated, each given one of said subscription television receivers comprising:

a timing mechanism including a motor and a rotatable cam, having an electrically conductive element positioned at some point on its periphery unique to said given receiver, which is coupled to and adapted to be rotated by said motor from a reference position to a starting position and then to and through each one of a multiplicity of different positions in time sequence;

means responsive to such actuation of said control in said given receiver for maintaining said motor energized to etect rotation of said cam from its reference position;

arresting means for arresting the movement of said cam when said cam reaches its starting position, while permitting said motor to remain energized;

means responsive to one of said interrogating signals occurring after said cam attains its starting position for releasing said arresting means thereby to permit said motor to advance said cam from its starting position and through each one of at least some of its multiplicity of different positions;

a pair of reply switch contacts, engaging and sensing the periphery of said cam, being electrically joined through said conductive element when said cam reaches a predetermined position unique to said given receiver;

and means responsive to the joining of said reply switch contacts for transmitting a reply signal back to s-aid central oflice, the time interval between said one interrogating signal and said reply signal thereby being of a duration unique to said given receiver to indicate at said central office that said reply signal originated at said given receiver.

15. In an interrogating system for sequentially examining in response to time-spaced interrogating signals transmitted from a central otlice a plurality of subscription television receivers, each of which includes a control that must be actuated by a subscriber in a predetermined manner to elect untilization of a received subscription -television program signal, to determine the particular ones of said receivers that have been so actuated, each given one of said subscription television receivers comprising:

a timing mechanism including a motor and rotatable cam, having a notch on its periphery, which is coupled to and adapted to be rotated by said motor from a reference position to a starting position and then to and through each one of a multiplicity of different positions in time sequence;

means responsive to such actuation of said control in said given receiver for maintaining said motor energized to effect rotation of said cam from its reference position;

arresting means including a cam following lever that is urged against and engages the periphery of said cam, said lever falling into said notch when said cam reaches its starting position to prevent further rotation of said cam;

means coupled between said motor and said cam for 32 permitting said motor to continue rotating even though said cam is held in its starting position by said arresting means; means responsive to lone of said interrogating signals occurring after said cam attains its starting position for moving said lever out of engagement with said notch to release said arresting means thereby to permit said motor to advance said cam from its starting position and through each one of at least some 'of its multiplicity of diierent positions; and means operable when -said cam subsequently reaches a predetermined position, unique to said given receiver, for transmitting a reply signal back to said central oice, the time interval between said one interrogating signal and said reply signal thereby being of a duration unique to said given receiver to indicate at siad central oce that said reply signal originated at said given receiver. 16. 'In an interrogating system for examining from a central oflice a plurality of subscription television receivers, each of which includes a control that must be actuated by a subscriber in a predetermined manner t-o elfect utilization of a received subscription television program signal to determine the particular ones of said receivers that lhave been so actuated, each given one of said subscription television receivers comprising:

enabling means responsive to such actuation of said control in said given receiver for enabling said given receiver to utilize said subscription television signal;

means operable in response to such actuation of said control in said given receiver for transmitting a signal to said central office to provide an indication that said given receiver is utilizing said subscription television signal;

and disabling means adapted to be remotely controlled from said central ofice for disabling said given receiver.

17. In an interrogating system for examining from a central office a plurality of subscription television receivers, each of which includes `a control that must be actuated by a subscriber in a predetermined manner to effect utilization of a received subscription television program signal, to determine the particular ones of said receivers that have been so actuated, each given one `of said subscription television receivers comprising:

enabling means responsive to such actuation of said control in said given receiver for enabling said given receiver to utilize said subscription television signal;

means operable in response to such actuation of said control -in said given receiver for transmitting a signal to said central oilice to provide an indication that said given receiver is utilizing said subscription television signal;

and disabling means to be remotely controlled from said central oice for selectively disabling said given receiver without aiecting any of the other subscription television receivers in said system.

18. In an interrogating system for examining from a central ofce a plurality of subscription television .receivers in response to an interrogating signal Atransmitted from said central office to said receivers over a common electrically conductive connection, each of said receivers including a control that must be actuated by -a subscriber in a predetermined manner to effect utilization of a received subscription television program signal, to determine the particular ones of said receivers that have been so actuated, each given one of said subscription television receivers comprising:

enabling means responsive to such actuation of said control in said given receiver -for enabling said given receiver to utilize said subscription television signal; means operable responsive to such actuation of said control in said given receiver and also to said interrogating signal for transmitting a reply signal back to said central oflice over said common conductive 

